The present invention relates to wave propagation signal transmission devices of a novel type, usable in particular for the construction of wide band H.F power amplifiers.
The H.F. amplifier with wide passband (from LF to VHF) is customarily obtained with the aid of power tubes functioning with localised constants. These tubes possess dimensions and physical and electrical characteristics which are defined pointwise (current, input and output capacitances/inductances, amplifying ability between an input level and an output level, etc).
It has been proposed to increase the dimensions of vacuum tubes and the surface area of electrodes with the aim of enhancing the power amplification. The corresponding increase in input and output capacitances has the unfavourable effect of substantially reducing the passband of the amplifier tube (generally defined with respect to a power attenuation of -3db). In practice, the product "power gain.times.passband" is substantially constant for a given tube used alone or in an assembly of several tubes mounted in parallel.
It has also been proposed to construct an amplifier in part with distributed constants by constituting a distribution line in which the localised constants which the tubes represent are associated with complementary localised inductive elements to create a propagation line at input (the input capacitances associated with these inductances thereby producing a low-pass filter). Similarly, the output capacitances of the tubes are associated with localised inductive elements to create a propagation line at output connected to the unit's useful load. The U.S. Pat. No. 3,808,546 describes a configuration of this type in which a complete unit of several tubes is placed in a vacuum inside a common enclosure.
This solution, although representing an improvement, also has its limits in the field of HF amplification owing to the high values of the input and output capacitances of the tubes.